Its major commercial use is for pesticides (insects, 

 weeds, fungi). Arsenic is cumulative in the tissues 

 of many organisms and, therefore, it eventually 

 exerts its effects even though the environmental 

 level is low. It has been demonstrated to be a pos- 

 sible carcinogen in water. 



Arsenic is found in seawater at a concentration 

 of about 0.003 mg/1. It has been found in marine 

 plants at concentrations up to 30 mg/1 and is high- 

 est in the brown algae. It is found in marine ani- 

 mals in a range of 0.005 to 0.3 mg/1. It is accumu- 

 lated by coelenterates, some mollusks, and 

 crustaceans (Vinogradov, 1953). It is moderately 

 toxic to plants and highly toxic to animals especi- 

 ally as AsHa. 



Arsenic trioxide, which also is exceedingly toxic, 

 was studied in concentrations of 1.96 to 40 mg/1 

 and found to be harmful to fish or other aquatic 

 life. Work by the Washington Department of Fish- 

 eries (1944) on pink salmon has shown that at a 

 level of 5.3 mg/1 of AS2O3 for 8 days was extremely 

 harmful to this species. Ellis (1937), using the 

 same compound on mussels at a level of 1 6 mg/I, 

 found it to be quite lethal in 3 to 16 days. Surber 

 and Meehan (1931) carried out an extensive study 

 on the toxicity of AsoO^ to many different fish food 

 organisms. Their results indicated that important 

 fish food organisms can tolerate an application rate 

 of 2 mg/1 of As.,03. The amount actually in the 

 water is considerably less. 



Cadmium. — The elemental form of cadmium 

 is insoluble in water. It occurs largely as the sulfide 

 which is often an impurity in zinc ores. 



Cadmium is found in seawater at a level of less 

 than 0.08 mg/1. Its level in marine plants is ap- 

 proximately 0.4 mg/1, while in marine animals a 

 range of 0.15 to 3 mg/1 has been found. It is low- 

 est in the calcareous tissues and is accumulated 

 within the viscera of the moUusk, Pecten novazet- 

 landicae (Brooks and Rumsby, 1965). Cadmium 

 is moderately toxic to all organisms and it is a 

 cumulative poison in mammals. 



Cadmium is used widely industrially to alloy 

 with copper, lead, silver, aluminum, and nickel. It 

 is also used in electroplating, ceramics, pigmenta- 

 tion, photography, and nuclear reactors. Cadmium 

 salts sometimes are used as insecticides and anti- 

 helminthics. The chloride, nitrate, and sulfate of 

 cadmium are highly soluble in water. The carbo- 

 nate and hydroxide are insoluble, thus cadmium 

 will be precipitated at high pH values. 



Most quantitative data on the toxicity of cad- 

 mium are based on specific salts of the metal. Ex- 

 pressed as cadmium, these data indicate that the 

 acute lethal level for fish varies from about 0.01 to 

 about 10 mg/1 depending on the test animal, the 



type of water, temperature, and time of exposure. 

 Cadmium acts synergistic ally with other substances 

 to increase toxicity. Concentrations of 0.03 mg/1 

 in combination with 0.15 mg/1 zinc causes mor- 

 tality of salmon fry (Hublou, et al., 1954) . 



Pringle (in press), in a study of adult American 

 Eastern oysters, Crassostrea virginica, found an 8- 

 week TL,„ value of 0.2 mg/1 of Cd^+[Cd(N03)2] 

 and a 15-week TLn, value of 0.1 mg/1. 



The most obvious effect, in addition to lethality, 

 was lack of shell growth. A similar study on the 

 clam, Mercenaria mercenaria, indicated that a 

 much longer period of exposure at the same con- 

 centration was required to kill half of the test 

 organisms. 



Chromium. — Chromium is found in seawater at 

 a concentration of 0.00005 mg/1. Marine plants 

 contain approximately 1.0 mg/1 while marine ani- 

 mals contain chromium within a range of 0.2 to 

 1.0 mg/1. Chromium compounds may be present 

 in wastes from many industrial processes or they 

 may be discharged in chromium-treated cooling 

 waters. The toxicity of chromium varies with the 

 species, temperature, pH, its valence, and synergis- 

 tic or antagonistic effects (especially with hard- 

 ness). Most evidence points to the fact that under 

 long-term exposure the hexavalent form is no more 

 toxic towards fish than the trivalent form. Doudor- 

 off and Katz (1953), studied the effect of Y^jCr^i^ 

 on mummichaugs and found that they tolerated a 

 200 mg/1 level in sea water for over a week. 



The effects of hexavalent chromium on photo- 

 synthesis by the giant kelp, Macrocystis pyrijera, 

 were as follows: at 1 mg/1 chromium, photosyn- 

 thesis was not diminished by 2 days contact. It 

 was reduced 10 to 20 percent by 5 days contact 

 and 20 to 30 percent after 7 to 9 days. The con- 

 centration of chromium required to cause a 50-per- 

 cent inactivation of photosynthesis in 4 days was 

 estimated at 5 mg/1 (Clendenning and North, 

 1958, 1960; North and Clendenning, 1958, 1959). 



Haydu (unpublished data) studied oyster mor- 

 talities and his results point out the long-term ef- 

 fects of low concentrations of chromium, molybde- 

 num, and nickel. The levels of all three metals were 

 in the range of 10 to 12 ^g/1 over a 2-year period. 

 In addition, his data indicated that there were sea- 

 sonal variations. The mortalities at these levels in-s 

 creased with an increase in temperature. Approxi- 

 mately 63 to 73 percent of the mortalities occurred 

 in the period of May through July, perhaps due to 

 increased physiological activity (increased feeding 

 and higher pumping rates) . 



This study substantiates the available evidence 

 indicating that as the environmental level of these 

 metals increases, the ingestion-elimination balance 



86 



